Vehicle control system

ABSTRACT

In a vehicle control system, a control unit of the vehicle control system executes a stop process by which the vehicle is parked in a prescribed stop area when it is detected that the control unit or the driver has become incapable of properly maintaining a traveling state of the vehicle. In the stop process, the control unit determines a plurality of available stop areas according to the vehicle surroundings and map information, and computes, for each available stop area, a cumulative travel risk obtained by accumulating a travel risk involved in traveling from a position of the vehicle when the stop process is initiated to each available stop area and a stop risk in stopping in each available stop area, the control unit determining a final stop area by comparing the cumulative travel risk with the stop risk in each available stop area sequentially from the nearest one.

TECHNICAL FIELD

The present invention relates to a vehicle control system configured forautonomous driving.

BACKGROUND ART

It is known in the field of autonomous driving, in case of an emergencywhere the vehicle operator is incapacitated or has otherwise becomeunable to properly drive the vehicle, to autonomously maneuver thevehicle to a place where the traffic is least likely to be disrupted,and such a manoeuver is known as a minimal risk maneuver (MRM). See U.S.Pat. No. 9,766,085B2, for instance. According to this prior art, uponoccurrence of an emergency situation where the system is required totake over the responsibility of driving the vehicle, and the vehiclehappens to be located in a place from which the vehicle is required toevacuate, the system selects a plurality of target positions to whichthe vehicle may evacuate. The system then computes the risk of stoppingat each position, and the risk of passing each position, and decides thetarget position to which the vehicle should evacuate. Once the targetposition is decided, the vehicle travels to the target position andcomes to a stop at the target position.

According to this prior art, the target position is decided as soon asthe need to evacuate the current position is determined. However,depending on the positions of the surrounding other vehicles, and thecondition of the target position, the target position may have ceased tobe suitable for the vehicle in the MRM situation to evacuate to by thetime the vehicle reaches the target position.

SUMMARY OF THE INVENTION

In view of such a problem of the prior art, a primary object of thepresent invention is to provide a vehicle control system that can decidea target position for a vehicle in an emergency situation to proceed toin an optimum fashion.

To achieve such an object, the present invention provides a vehiclecontrol system, comprising: a control unit (15) for steering,accelerating, and decelerating a vehicle; an occupant monitoring device(11) configured to monitor a driver of the vehicle; an externalenvironment recognition device (6) configured to acquire information onan environment surrounding the vehicle; and a map device (9) retainingmap information; wherein the control unit is configured to execute astop process by which the vehicle is parked in a prescribed stop areawhen it is detected that the control unit or the driver has becomeincapable of properly maintaining a traveling state of the vehicle, andwherein, in the stop process, the control unit determines a plurality ofavailable stop areas according to the information on the environmentsurrounding the vehicle and the map information, and computes, for eachavailable stop area, a cumulative travel risk obtained by accumulating atravel risk involved in traveling from a position of the vehicle whenthe stop process is initiated to each available stop area and a stoprisk in stopping in each available stop area, the control unitdetermining a final stop area by comparing the cumulative travel riskwith the stop risk in each available stop area sequentially from thenearest one.

If the vehicle can be safely brought to a stop in a certain stop areacan be determined by taking into account the cumulative travel risk intraveling to or through the stop area and the risk associated withcoming to a stop at the stop area. When the initially selected stop areais found to be unsuitable, the vehicle automatically travels to anotherstop area. The same process may be repeated in the next potential stoparea. As a result, the vehicle can be brought to a stop more safely andreliably.

Preferably, the control unit determines the available stop area at whichthe cumulative travel risk exceeds the stop risk as the final stop area,or alternatively, the control unit determines the available stop areaimmediately preceding the one at which the cumulative travel riskexceeds the stop risk as the final stop area.

Thereby, the vehicle can be brought to a stop in the stop area with aminimal risk.

Preferably, when a preceding vehicle is detected by the externalenvironment recognition device, the control unit causes the vehicle tofollow the preceding vehicle in each interval between adjoiningavailable stop areas.

Thereby, the vehicle is enabled to travel to a next stop area with aminimal risk.

Preferably, the cumulative travel risk increases monotonically with atravel distance or a travel time.

Since the cumulative travel risk increases as the travel distance ortravel time increases, the vehicle is prevented from continuing totravel indefinitely.

Preferably, the external environment recognition device is configured tocapture an image of road signs, and the control unit increases thecumulative travel risk as the image of road signs grows darker.

When the brightness of the image captured by the external environmentrecognition device is equal to or less than a predetermined value, thepossibility that road markings cannot be detected increases, and thecumulative travel risk may be increased accordingly. Thus, the higherthe possibility that the road marking cannot be detected, the more thevehicle is prevented from continuing to travel. Therefore, if there is ahigh possibility that the road signs cannot be detected, the vehicle canbe brought to a stop more quickly.

Preferably, the control unit increases the cumulative travel risk foreach unit travel distance more at night than in daytime.

Thus, the cumulative travel risk is increased at night which is likelyto involve a higher risk is traveling so that the vehicle can be broughtto a stop more safely.

Preferably, the control unit increases the cumulative travel risk foreach unit travel distance more on a rainy day than on a fine day.

Thus, the cumulative travel risk is increased on a rainy day than on afine day in view of a higher risk in traveling on a rainy day so thatthe vehicle can be brought to a stop more safely.

Preferably, the occupant monitoring device is configured to detect anoccupant other than a driver, and the control unit increases thecumulative travel risk for each unit travel distance more when theoccupant other than the driver is detected than when the occupant otherthan the driver is not detected.

By thus bringing the vehicle to a stop more quickly when the occupantother than the driver is detected, the occupant is enabled to take overthe driving more quickly.

Preferably, the external environment recognition device is configured todetect a following vehicle, and the control unit increases thecumulative travel risk for each unit travel distance more when thefollowing vehicle is detected as the own vehicle is about to come to astop in the next available stop area than when the following vehicle isnot detected.

By thus computing the cumulative travel risk to be larger than when thefollowing vehicle is detected than when the following vehicle is notdetected, the vehicle can be brought to a stop more safely by reducingthe possibility of a rear end collision by the following vehicle.

Preferably, the external environment recognition device is configured todetect an inter-vehicle distance between the own vehicle and a followingvehicle, and the control unit increases the cumulative travel risk foreach unit travel distance more when the inter-vehicle distance betweenthe following vehicle and the own vehicle is equal to or lower than aprescribed value than when the inter-vehicle distance is greater thanthe prescribed value.

By taking into account the inter-vehicle distance between the ownvehicle and the following vehicle, the risk of a rear end collision bythe following vehicle can be more accurately evaluated.

Preferably, the control unit increases the cumulative travel risk foreach unit travel distance more when the vehicle is traveling in a fastlane than when the vehicle is traveling in a slow lane.

When the vehicle is traveling in a fast lane, lane changes will berequired for the vehicle to reach the stop area. Thereby, by taking intoaccount if the vehicle is in a fast lane or not at the start of the stopprocess, the vehicle can be brought to a stop more safely.

Preferably, the control unit increases the cumulative travel risk in apart of a road where lanes are restricted.

A restriction in lanes means a higher risk for the vehicle due tomerging of vehicles from the blocked or otherwise restricted lane.Thereby, by taking into account of the presence of a restriction inlanes, the vehicle can be brought to a stop more safely.

Preferably, the control unit determines the stop risk at each availablestop area from the map information.

Thereby, the stop risk at each available stop area can be easilyevaluated.

Preferably, the control unit increases the cumulative travel risk in anarrow part of a road.

A narrow part of a road tends to increase the risk in traveling for thevehicle. Therefore, by taking into account of the presence of a narrowpart of a road, the vehicle can be brought to a stop more safely.

Preferably, the control unit increases the cumulative travel risk in apart of the route where past data indicates a high frequency of lanechanges.

If lane changes occur at a high frequency in a certain part of theroute, it means that this part of the route causes a high risk for thevehicle. Therefore, by taking into account of the frequency of lanechanges in selected parts of the route, the vehicle can be brought to astop more safely.

The present invention thus provides a vehicle control system that candecide a target position for a vehicle in an emergency situation toproceed to in an optimum fashion.

BRIEF DESCRIPTION OF THE DRAWING(S)

FIG. 1 is a functional block diagram of a vehicle on which a vehiclecontrol system according to the present invention is mounted;

FIG. 2 is a flowchart of a stop process;

FIG. 3 is a flowchart of a stop area determination process;

FIG. 4 is a flowchart of a stop position determination process;

FIG. 5 is a diagram illustrating the movement of a vehicle in the stopprocess and the risks involved in traveling and stopping in availableareas during the daytime on a clear day; and

FIG. 6 is a diagram illustrating the movement of the vehicle in the stopprocess and the risks involved in traveling and stopping in availableareas during the nighttime on a rainy day.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

A vehicle control system according to a preferred embodiment of thepresent invention is described in the following with reference to theappended drawings. The following disclosure is based on left-handtraffic. In the case of right-hand traffic, the left and the right inthe disclosure will be reversed.

First Embodiment

As shown in FIG. 1, the vehicle control system 1 according to thepresent invention is a part of a vehicle system 2 mounted on a vehicle.The vehicle system 2 includes a power unit 3, a brake device 4, asteering device 5, an external environment recognition device 6, avehicle sensor 7, a communication device 8, a navigation device 9 (mapdevice), a driving operation device 10, an occupant monitoring device11, an HMI 12 (Human Machine Interface), an autonomous driving levelswitch 13, an external notification device 14, and a control unit 15.These components of the vehicle system 2 are connected to one another sothat signals can be transmitted between them via a communication meanssuch as CAN 16 (Controller Area Network).

The power unit 3 is a device for applying a driving force to thevehicle, and may include a power source and a transmission unit. Thepower source may consist of an internal combustion engine such as agasoline engine and a diesel engine, an electric motor or a combinationof these. The brake device 4 is a device that applies a braking force tothe vehicle, and may include a brake caliper that presses a brake padagainst a brake rotor, and an electrically actuated hydraulic cylinderthat supplies hydraulic pressure to the brake caliper. The brake device4 may also include a parking brake device. The steering device 5 is adevice for changing a steering angle of the wheels, and may include arack-and-pinion mechanism that steers the front wheels, and an electricmotor that drives the rack-and-pinion mechanism. The power unit 3, thebrake device 4, and the steering device 5 are controlled by the controlunit 15.

The external environment recognition device 6 is a device that detectsobjects located outside of the vehicle. The external environmentrecognition device 6 may include a sensor that captures electromagneticwaves or light from around the vehicle to detect objects outside of thevehicle, and may consist of a radar 17, a lidar 18, an external camera19, or a combination of these. The external environment recognitiondevice 6 may also be configured to detect objects outside of the vehicleby receiving a signal from a source outside of the vehicle. Thedetection result of the external environment recognition device 6 isforwarded to the control unit 15.

The radar 17 emits radio waves such as millimeter waves to thesurrounding area of the vehicle, and detects the position (distance anddirection) of an object by capturing the reflected wave. Preferably, theradar 17 includes a front radar that radiates radio waves toward thefront of the vehicle, a rear radar that radiates radio waves toward therear of the vehicle, and a pair of side radars that radiates radio wavesin the lateral directions.

The lidar 18 emits light such as an infrared ray to the surrounding partof the vehicle, and detects the position (distance and direction) of anobject by capturing the reflected light. At least one lidar 18 isprovided at a suitable position of the vehicle.

The external camera 19 can capture the image of the surrounding objectssuch as vehicles, pedestrians, guardrails, curbs, walls, median strips,road shapes, road signs, road markings painted on the road, and thelike. The external camera 19 may consist of a digital camera using asolid-state imaging device such as a CCD and a CMOS. At least oneexternal camera 19 is provided at a suitable position of the vehicle.The external camera 19 preferably includes a front camera that imagesthe front of the vehicle, a rear camera that images the rear of thevehicle and a pair of side cameras that image the lateral views from thevehicle. The external camera 19 may consist of a stereo camera that cancapture a three-dimensional image of the surrounding objects.

The vehicle sensor 7 may include a vehicle speed sensor that detects thetraveling speed of the vehicle, an acceleration sensor that detects theacceleration of the vehicle, a yaw rate sensor that detects an angularvelocity of the vehicle around a vertical axis, a direction sensor thatdetects the traveling direction of the vehicle, and the like. The yawrate sensor may consist of a gyro sensor.

The communication device 8 allows communication between the control unit15 which is connected to the navigation device 9 and other vehiclesaround the own vehicle as well as servers located outside the vehicle.The control unit 15 can perform wireless communication with thesurrounding vehicles via the communication device 8. For instance, thecontrol unit 15 can communicate with a server that provides trafficregulation information via the communication device 8, and with anemergency call center that accepts an emergency call from the vehiclealso via the communication device 8. Further, the control unit 15 cancommunicate with a portable terminal carried by a person such as apedestrian present outside the vehicle via the communication device 8.

The navigation device 9 is able to identify the current position of thevehicle, and performs route guidance to a destination and the like, andmay include a GNSS receiver 21, a map storage unit 22, a navigationinterface 23, and a route determination unit 24. The GNSS receiver 21identifies the position (latitude and longitude) of the vehicleaccording to a signal received from artificial satellites (positioningsatellites). The map storage unit 22 may consist of a per se knownstorage device such as a flash memory and a hard disk, and stores orretains map information. The navigation interface 23 receives an inputof a destination or the like from the user, and provides variousinformation to the user by visual display and/or speech. The navigationinterface 23 may include a touch panel display, a speaker, and the like.In another embodiment, the GNSS receiver 21 is configured as a part ofthe communication device 8. The map storage unit 22 may be configured asa part of the control unit 15 or may be configured as a part of anexternal server that can communicate with the control unit 15 via thecommunication device 8.

The map information may include a wide range of road information whichmay include, not exclusively, road types such as expressways, tollroads, national roads, and prefectural roads, the number of lanes of theroad, road markings such as the center position of each lane(three-dimensional coordinates including longitude, latitude, andheight), road division lines and lane lines, the presence or absence ofsidewalks, curbs, fences, etc., the locations of intersections, thelocations of merging and branching points of lanes, the areas ofemergency parking zones, the width of each lane, and traffic signsprovided along the roads. The map information may also include trafficregulation information, address information (address/postal code),facility information, telephone number information, and the like.

The route determination unit 24 determines a route to the destinationbased on the position of the vehicle specified by the GNSS receiver 21,the destination input from the navigation interface 23, and the mapinformation. When determining the route, in addition to the route, theroute determination unit 24 determines the target lane which the vehiclewill travel in by referring to the merging and branching points of thelanes in the map information.

The driving operation device 10 receives an input operation performed bythe driver to control the vehicle. The driving operation device 10 mayinclude a steering wheel, an accelerator pedal, and a brake pedal.Further, the driving operation device 10 may include a shift lever, aparking brake lever, and the like. Each element of the driving operationdevice 10 is provided with a sensor for detecting an operation amount ofthe corresponding operation. The driving operation device 10 outputs asignal indicating the operation amount to the control unit 15.

The occupant monitoring device 11 monitors the state of the occupant inthe passenger compartment. The occupant monitoring device 11 includes,for example, an internal camera 26 that images an occupant sitting on aseat in the vehicle cabin, and a grip sensor 27 provided on the steeringwheel. The internal camera 26 is a digital camera using a solid-stateimaging device such as a CCD and a CMOS. The grip sensor 27 is a sensorthat detects if the driver is gripping the steering wheel, and outputsthe presence or absence of the grip as a detection signal. The gripsensor 27 may be formed of a capacitance sensor or a piezoelectricdevice provided on the steering wheel. The occupant monitoring device 11may include a heart rate sensor provided on the steering wheel or theseat, or a seating sensor provided on the seat. In addition, theoccupant monitoring device 11 may be a wearable device that is worn bythe occupant, and can detect the vital information of the driverincluding at least one of the heart rate and the blood pressure of thedriver. In this conjunction, the occupant monitoring device 11 may beconfigured to be able to communicate with the control unit 15 via a perse known wireless communication means. The occupant monitoring device 11outputs the captured image and the detection signal to the control unit15.

The external notification device 14 is a device for notifying to peopleoutside of the vehicle by sound and/or light, and may include a warninglight and a horn. A headlight (front light), a taillight, a brake lamp,a hazard lamp, and a vehicle interior light may function as a warninglight.

The HMI 12 notifies the occupant of various kinds of information byvisual display and speech, and receives an input operation by theoccupant. The HMI 12 may include at least one of a display device 31such as a touch panel and an indicator light including an LCD or anorganic EL, a sound generator 32 such as a buzzer and a speaker, and aninput interface 33 such as a GUI switch on the touch panel and amechanical switch. The navigation interface 23 may be configured tofunction as the HMI 12.

The autonomous driving level switch 13 is a switch that activatesautonomous driving as an instruction from the driver. The autonomousdriving level switch 13 may be a mechanical switch or a GUI switchdisplayed on the touch panel, and is positioned in a suitable part ofthe cabin. The autonomous driving level switch 13 may be formed by theinput interface 33 of the HMI 12 or may be formed by the navigationinterface 23.

The control unit 15 may consist of an electronic control unit (ECU)including a CPU, a ROM, a RAM, and the like. The control unit 15executes various types of vehicle control by executing arithmeticprocesses according to a computer program executed by the CPU. Thecontrol unit 15 may be configured as a single piece of hardware, or maybe configured as a unit including a plurality of pieces of hardware. Inaddition, at least a part of each functional unit of the control unit 15may be realized by hardware such as an LSI, an ASIC, and an FPGA, or maybe realized by a combination of software and hardware.

The control unit 15 is configured to execute autonomous driving controlof at least level 0 to level 3 by combining various types of vehiclecontrol. The level is based on the definition of SAE J3016, and isdetermined in relation to the degree of machine intervention in thedriving operation of the driver and in the monitoring of the surroundingenvironment of the vehicle.

In autonomous driving of level 0, the control unit 15 does not controlthe vehicle, and the driver performs all of the driving operations.Thus, autonomous driving of level 0 means a manual driving.

In autonomous driving of level 1, the control unit 15 executes a certainpart of the driving operation, and the driver performs the remainingpart of the driving operation. For example, autonomous driving level 1includes constant speed traveling, inter-vehicle distance control (ACC;Adaptive Cruise Control) and lane keeping assist control (LKAS; LaneKeeping Assistance System). The level 1 autonomous driving is executedwhen various devices (for example, the external environment recognitiondevice 6 and the vehicle sensor 7) required for executing the level 1autonomous driving are all properly functioning.

In autonomous driving of level 2, the control unit 15 performs theentire driving operation. The level 2 autonomous driving is performedonly when the driver monitors the surrounding environment of thevehicle, the vehicle is within a designated area, and the variousdevices required for performing the level 2 autonomous driving are allfunctioning properly.

In level 3 autonomous driving, the control unit 15 performs the entiredriving operation. The level 3 autonomous driving requires the driver tomonitor or be aware of the surrounding environment when required, and isexecuted only when the vehicle is within a designated area, and thevarious devices required for performing the level 3 autonomous drivingare all functioning properly. The conditions under which the level 3autonomous driving is executed may include that the vehicle is travelingon a congested road. Whether the vehicle is traveling on a congestedroad or not may be determined based on traffic regulation informationprovided from a server outside of the vehicle, or, alternatively, thatthe vehicle speed detected by the vehicle speed sensor is determined tobe lower than a predetermined slowdown determination value (for example,30 km/h) over a predetermined time period.

Thus, in the autonomous driving of levels 1 to 3, the control unit 15executes at least one of the steering, the acceleration, thedeceleration, and the monitoring of the surrounding environment. When inthe autonomous driving mode, the control unit 15 executes the autonomousdriving of level 1 to level 3. Hereinafter, the steering, acceleration,and deceleration operations are collectively referred to as drivingoperation, and the driving and the monitoring of the surroundingenvironment may be collectively referred to as driving.

In the present embodiment, when the control unit 15 has received aninstruction to execute autonomous driving via the autonomous drivinglevel switch 13, the control unit 15 selects the autonomous drivinglevel that is suitable for the environment of the vehicle according tothe detection result of the external environment recognition device 6and the position of the vehicle acquired by the navigation device 9, andchanges the autonomous driving level as required. However, the controlunit 15 may also change the autonomous driving level according the inputto the autonomous driving level switch 13.

As shown in FIG. 1, the control unit 15 includes an autonomous drivingcontrol unit 35, an abnormal state determination unit 36, a statemanagement unit 37, a travel control unit 38, and a storage unit 39.

The autonomous driving control unit 35 includes an external environmentrecognition unit 40, a vehicle position recognition unit 41, and anaction plan unit 42. The external environment recognition unit 40recognizes an obstacle located around the vehicle, the shape of theroad, the presence or absence of a sidewalk, and road signs based on thedetection result of the external environment recognition device 6. Theobstacles include, not exclusively, guardrails, telephone poles,surrounding vehicles, and pedestrians. The external environmentrecognition unit 40 can acquire the state of the surrounding vehicles,such as the position, speed, and acceleration of each surroundingvehicle from the detection result of the external environmentrecognition device 6. The position of each surrounding vehicle may berecognized as a representative point such as a center of gravityposition or a corner positions of the surrounding vehicle, or an arearepresented by the contour of the surrounding vehicle.

The vehicle position recognition unit 41 recognizes a traveling lane,which is a lane in which the vehicle is traveling, and a relativeposition and an angle of the vehicle with respect to the traveling lane.The vehicle position recognition unit 41 may recognize the travelinglane based on the map information stored in the map storage unit 22 andthe position of the vehicle acquired by the GNSS receiver 21. Inaddition, the lane markings drawn on the road surface around the vehiclemay be extracted from the map information, and the relative position andangle of the vehicle with respect to the traveling lane may berecognized by comparing the extracted lane markings with the lanemarkings captured by the external camera 19.

The action plan unit 42 sequentially creates an action plan for drivingthe vehicle along the route. More specifically, the action plan unit 42first determines a set of events for traveling on the target lanedetermined by the route determination unit 24 without the vehicle cominginto contact with an obstacle. The events may include a constant speedtraveling event in which the vehicle travels in the same lane at aconstant speed, a preceding vehicle following event in which the vehiclefollows a preceding vehicle at a certain speed which is equal to orlower than a speed selected by the driver or a speed which is determinedby the prevailing environment, a lane changing event in which thevehicle change lanes, a passing event in which the vehicle passes apreceding vehicle, a merging event in which the vehicle merge into thetraffic from another road at a junction of the road, a diverging eventin which the vehicle travels into a selected road at a junction of theroad, an autonomous driving end event in which autonomous driving isended, and the driver takes over the driving operation, and a stop eventin which the vehicle is brought to a stop when a certain condition ismet, the condition including a case where the control unit 15 or thedriver has become incapable of continuing the driving operation.

The conditions under which the action plan unit 42 invokes the stopevent include the case where an input to the internal camera 26, thegrip sensor 27, or the autonomous driving level switch 13 in response toan intervention request (a hand-over request) to the driver is notdetected during autonomous driving. The intervention request is awarning to the driver to take over a part of the driving, and to performat least one of the driving operation and the monitoring of theenvironment corresponding to the part of the driving that is to behanded over. The condition under which the action plan unit 42 invokesthe stop even include the case where the action plan unit 42 hasdetected that the driver has become incapable of performing the drivingwhile the vehicle is traveling due to a physiological ailment accordingto the signal from a pulse sensor, the internal camera or the like.

During the execution of these events, the action plan unit 42 may invokean avoidance event for avoiding an obstacle or the like based on thesurrounding conditions of the vehicle (existence of nearby vehicles andpedestrians, lane narrowing due to road construction, etc.).

The action plan unit 42 generates a target trajectory for the vehicle totravel in the future corresponding to the selected event. The targettrajectory is obtained by sequentially arranging trajectory points thatthe vehicle should trace at each time point. The action plan unit 42 maygenerate the target trajectory based on the target speed and the targetacceleration set for each event. At this time, the information on thetarget speed and the target acceleration is determined for each intervalbetween the trajectory points.

The travel control unit 38 controls the power unit 3, the brake device4, and the steering device 5 so that the vehicle traces the targettrajectory generated by the action plan unit 42 according to theschedule also generated by the action plan unit 42.

The storage unit 39 is formed by a ROM, a RAM, or the like, and storesinformation required for the processing by the autonomous drivingcontrol unit 35, the abnormal state determination unit 36, the statemanagement unit 37, and the travel control unit 38.

The abnormal state determination unit 36 includes a vehicle statedetermination unit 51 and an occupant state determination unit 52. Thevehicle state determination unit 51 analyzes signals from variousdevices (for example, the external environment recognition device 6 andthe vehicle sensor 7) that affect the level of the autonomous drivingthat is being executed, and detects the occurrence of an abnormality inany of the devices and units that may prevent a proper execution of theautonomous driving of the level that is being executed.

The occupant state determination unit 52 determines if the driver is inan abnormal state or not according to a signal from the occupantmonitoring device 11. The abnormal state includes the case where thedriver is unable to properly steer the vehicle in autonomous driving oflevel 1 or lower that requires the driver to steer the vehicle. That thedriver is unable to steer the vehicle in autonomous driving of level 1or lower could mean that the driver is not holding the steering wheel,the driver is asleep, the driver is incapacitated or unconscious due toillness or injury, or the driver is under a cardiac arrest. The occupantstate determination unit 52 determines that the driver is in an abnormalstate when there is no input to the grip sensor 27 from the driver whilein autonomous driving of level 1 or lower that requires the driver tosteer the vehicle. Further, the occupant state determination unit 52 maydetermine the open/closed state of the driver's eyelids from the faceimage of the driver that is extracted from the output of the internalcamera 26. The occupant state determination unit 52 may determine thatthe driver is asleep, under a strong drowsiness, unconscious or under acardiac arrest so that the drive is unable to properly drive thevehicle, and the driver is in an abnormal condition when the driver'seyelids are closed for more than a predetermined time period, or whenthe number of times the eyelids are closed per unit time interval isequal to or greater than a predetermined threshold value. The occupantstate determination unit 52 may further acquire the driver's posturefrom the captured image to determine that the driver's posture is notsuitable for the driving operation or that the posture of the driverdoes not change for a predetermined time period. It may well mean thatthe driver is incapacitated due to illness or injury, and in an abnormalcondition.

In the case of autonomous driving of level 2 or lower, the abnormalcondition includes a situation where the driver is neglecting the dutyto monitor the environment surrounding the vehicle. This situation mayinclude either the case where the driver is not holding or gripping thesteering wheel or the case where the driver's line of sight is notdirected in the forward direction. The occupant state determination unit52 may detect the abnormal condition where the driver is neglecting tomonitor the environment surrounding the vehicle when the output signalof the grip sensor 27 indicates that the driver is not holding thesteering wheel. The occupant state determination unit 52 may detect theabnormal condition according to the image captured by the internalcamera 26. The occupant state determination unit 52 may use a per seknown image analysis technique to extract the face region of the driverfrom the captured image, and then extracts the iris parts (hereinafter,iris) including the inner and outer corners of the eyes and pupils fromthe extracted face area. The occupant state determination unit 52 maydetect the driver's line of sight according to the positions of theinner and outer corners of the eyes, the iris, the outline of the iris,and the like. It is determined that the driver is neglecting the duty tomonitor the environment surrounding the vehicle when the driver's lineof sight is not directed in the forward direction.

In addition, in the autonomous driving at a level where the drive is notrequired to monitor the surrounding environment or in the autonomousdriving of level 3, an abnormal condition refers to a state in which thedriver cannot promptly take over the driving when a driving takeoverrequest is issued to the driver. The state where the driver cannot takeover the driving includes the state where the system cannot bemonitored, or, in other words, where the driver cannot monitor a screendisplay that may be showing an alarm display such as when the driver isasleep, and when the driver is not looking ahead. In the presentembodiment, in the level 3 autonomous driving, the abnormal conditionincludes a case where the driver cannot perform the duty of monitoringthe surrounding environment of the vehicle even though the driver isnotified to monitor the surrounding environment of the vehicle. In thepresent embodiment, the occupant state determination unit 52 displays apredetermined screen on the display device 31 of the HMI 12, andinstructs the driver to look at the display device 31. Thereafter, theoccupant state determination unit 52 detects the driver's line of sightwith the internal camera 26, and determines that the driver is unable tofulfill the duty of monitoring the surrounding environment of thevehicle if driver's line of sight is not facing the display device 31 ofthe HMI 12.

The occupant state determination unit 52 may detect if the driver isgripping the steering wheel according to the signal from the grip sensor27, and if the driver is not gripping the steering wheel, it can bedetermined that the vehicle is in an abnormal state in which the duty ofmonitoring the surrounding environment the vehicle is being neglected.Further, the occupant state determination unit 52 determines if thedriver is in an abnormal state according to the image captured by theinternal camera 26. For example, the occupant state determination unit52 extracts a driver's face region from the captured image by using aper se known image analysis means. The occupant state determination unit52 may further extract iris parts (hereinafter, iris) of the driverincluding the inner and outer corners of the eyes and pupils from theextracted face area. The occupant state determination unit 52 obtainsthe driver's line of sight according to the extracted positions of theinner and outer corners of the eyes, the iris, the outline of the iris,and the like. It is determined that the driver is neglecting the duty tomonitor the environment surrounding the vehicle when the driver's lineof sight is not directed in the forward direction.

The state management unit 37 selects the level of the autonomous drivingaccording to at least one of the own vehicle position, the operation ofthe autonomous driving level switch 13, and the determination result ofthe abnormal state determination unit 36. Further, the state managementunit 37 controls the action plan unit 42 according to the selectedautonomous driving level, thereby performing the autonomous drivingaccording to the selected autonomous driving level. For example, whenthe state management unit 37 has selected the level 1 autonomousdriving, and a constant speed traveling control is being executed, theevent to be determined by the action plan unit 42 is limited only to theconstant speed traveling event.

The state management unit 37 raises and lowers the autonomous drivinglevel as required in addition to executing the autonomous drivingaccording to the selected level.

More specifically, the state management unit 37 raises the level whenthe condition for executing the autonomous driving at the selected levelis met, and an instruction to raise the level of the autonomous drivingis input to the autonomous driving level switch 13.

When the condition for executing the autonomous driving of the currentlevel ceases to be satisfied, or when an instruction to lower the levelof the autonomous driving is input to the autonomous driving levelswitch 13, the state management unit 37 executes an intervention requestprocess. In the intervention request process, the state management unit37 first notifies the driver of a handover request. The notification tothe driver may be made by displaying a message or image on the displaydevice 31 or generating a speech or a warning sound from the soundgenerator 32. The notification to the driver may continue for apredetermined period of time after the intervention request process isstarted or may be continued until an input is detected by the occupantmonitoring device 11.

The condition for executing the autonomous driving of the current levelceases to be satisfied when the vehicle has moved to an area where onlythe autonomous driving of a level lower than the current level ispermitted, or when the abnormal state determination unit 36 hasdetermined that an abnormal condition that prevents the continuation ofthe autonomous driving of the current level has occurred to the driveror the vehicle.

Following the notification to the driver, the state management unit 37detects if the internal camera 26 or the grip sensor 27 has received aninput from the driver indicating a takeover of the driving. Thedetection of the presence or absence of an input to take over thedriving is determined in a way that depends on the level that is to beselected. When moving to level 2, the state management unit 37 extractsthe driver's line of sight from the image acquired by the internalcamera 26, and when the driver's line of sight is facing the front ofthe vehicle, it is determined that an input indicating the takeover ofthe driving by the driver is received. When moving to level 1 or level0, the state management unit 37 determines that there is an inputindicating an intent to take over the driving when the grip sensor 27has detected the gripping of the steering wheel by the driver. Thus, theinternal camera 26 and the grip sensor 27 function as an interventiondetection device that detects an intervention of the driver to thedriving. Further, the state management unit 37 may detect if there is aninput indicating an intervention of the driver to the driving accordingto the input to the autonomous driving level switch 13.

The state management unit 37 lowers the autonomous driving level when aninput indicating an intervention to the driving is detected within apredetermined period of time from the start of the intervention requestprocess. At this time, the level of the autonomous driving after thelowering of the level may be level 0, or may be the highest level thatcan be executed.

The state management unit 37 causes the action plan unit 42 to generatea stop event when an input corresponding to the driver's intervention tothe driving is not detected within a predetermined period of time afterthe execution of the intervention request process. The stop event is anevent in which the vehicle is brought to a stop at a safe position (forexample, an emergency parking zone, a roadside zone, a roadsideshoulder, a parking area, etc.) while the vehicle control isdegenerated. Here, a series of procedures executed in the stop event maybe referred to as MRM (Minimum Risk Maneuver).

When the stop event is invoked, the control unit 15 shifts from theautonomous driving mode to the automatic stop mode, and the action planunit 42 executes the stop process. Hereinafter, an outline of the stopprocess is described with reference to the flowchart of FIG. 2.

In the stop process, a notification process is first executed (ST1). Inthe notification process, the action plan unit 42 operates the externalnotification device 14 to notify the people outside of the vehicle. Forexample, the action plan unit 42 activates a horn included in theexternal notification device 14 to periodically generate a warningsound. The notification process continues until the stop process ends.After the notification process has ended, the action plan unit 42 maycontinue to activate the horn to generate a warning sound depending onthe situation.

Then, a degeneration process is executed (ST2). The degeneration processis a process of restricting events that can be invoked by the actionplan unit 42. The degeneration process may prohibit a lane change eventto a passing lane, a passing event, a merging event, and the like.Further, in the degeneration process, the speed upper limit and theacceleration upper limit of the vehicle may be more limited in therespective events as compared with the case where the stop process isnot performed.

Next, a stop area determination process is executed (ST3). The stop areadetermination process refers to the map information based on the currentposition of the own vehicle, and extracts a plurality of available stopareas (candidates for the stop area or potential stop areas) suitablefor stopping, such as road shoulders and evacuation spaces in thetraveling direction of the own vehicle. Then, one of the available stopareas is selected as the stop area by taking into account the size ofthe stop area, the distance to the stop area, and the like.

Next, a moving process is executed (ST4). In the moving process, a routefor reaching the stop area is determined, various events along the routeleading to the stop area are generated, and a target trajectory isdetermined. The travel control unit 38 controls the power unit 3, thebrake device 4, and the steering device 5 based on the target trajectorydetermined by the action plan unit 42. The vehicle then travels alongthe route and reaches the stop area.

Next, a stop position determination process is executed (ST5). In thestop position determination process, the stop position is determinedbased on obstacles, road markings, and other objects located around thevehicle recognized by the external environment recognition unit 40. Inthe stop position determination process, it is possible that the stopposition cannot be determined in the stop area due to the presence ofsurrounding vehicles and obstacles. When the stop position cannot bedetermined in the stop position determination process (No in ST6), thestop area determination process (ST3), the movement process (ST4), andthe stop position determination process (ST5) are sequentially repeated.

If the stop position can be determined in the stop positiondetermination process (Yes in ST6), a stop execution process is executed(ST7). In the stop execution process, the action plan unit 42 generatesa target trajectory based on the current position of the vehicle and thetargeted stop position. The travel control unit 38 controls the powerunit 3, the brake device 4, and the steering device 5 based on thetarget trajectory determined by the action plan unit 42. The vehiclethen moves toward the stop position and stops at the stop position.

After the stop execution process is executed, a stop maintaining processis executed (ST8). In the stop maintaining process, the travel controlunit 38 drives the parking brake device according to a command from theaction plan unit 42 to maintain the vehicle at the stop position.Thereafter, the action plan unit 42 may transmit an emergency call tothe emergency call center by the communication device 8. When the stopmaintaining process is completed, the stop process ends.

In the present embodiment, the vehicle control system 1 includes anexternal environment recognition device 6, a navigation device 9 (mapdevice), an occupant monitoring device 11, and a control unit 15. Thecontrol unit 15 is configured to compute a cumulative travel risk whichthe traveling of the vehicle incurs as a numerical value. The cumulativetravel risk is accumulated from the time point of initiating the stopprocess, and is evaluated at each available stop area.

The details of the stop area determination process are described in thefollowing with reference to FIG. 3. As a part of the stop areadetermination process, the cumulative risk is computed. In the followingdiscussion, it is assumed that the time duration of the stop process issufficiently short, and there is no change in the weather or in thedistinction between daytime and nighttime.

The action plan unit 42 determines a plurality of available stop areasin the first step ST11 of the stop area determination process. Morespecifically, the action plan unit 42 searches for available stop areaswhich are suitable for at least temporarily parking the vehicle, such asa road shoulder of a road on the route to a destination according to themap information. When the determination of available stop areas iscompleted, the action plan unit 42 executes step ST12.

In step ST12, the action plan unit 42 computes the distance on the routebetween the start position X and each stop area determined in step ST11by referring to the map information. The computed distance correspondsto the travel distance of the vehicle S when the vehicle S travels fromthe start position to the corresponding available stop area along theroute determined by the navigation device 9. In the present embodiment,the action plan unit 42 computes the distance on the route from thestart position to each available stop area in kilometers (km). When thecomputation of the distances ends, the action plan unit 42 executes stepST13.

The action plan unit 42 computes an external object recognitioncoefficient in step ST13. The external object recognition coefficient isa numerical value indicating the difficulty of detecting an object inthe environment where the vehicle is traveling. In the presentembodiment, the external object recognition coefficient indicates thedifficulty for the external environment recognition unit 40 to detect aroad sign from the image captured by the external camera 19, and thistypically depends on the brightness of the image captured by theexternal camera 19.

The brightness here indicates the brightness of the object, and is anumerical value that increases as the brightness increases. The externalobject recognition coefficient approaches 1 as the brightness increases,and increases as the brightness decreases. More specifically, theexternal object recognition coefficient is set to 1 when the vehicle istraveling in an environment where the outside of the vehicle is bright,and the road marking and the road signs can be reliably recognized bythe external environment recognition unit 40. As the outside of thevehicle becomes darker and it becomes harder to recognize the roadmarking or the like, the external object recognition coefficientincreases in value. For example, the external object recognitioncoefficient is set to 1 when the vehicle S is traveling in the daytimeand the weather is fine, and the external object recognition coefficientis set to a value greater than 1 when the vehicle is traveling in thenighttime and the weather is poor due to rain, snow, hail, or fog.

In the present embodiment, in step ST13, the action plan unit 42computes the external object recognition coefficient according to a timecoefficient associated with time and a weather coefficient associatedwith weather. More specifically, first, the action plan unit 42 connectsto an external time server (NTP server) via the communication device 8and acquires the current time. Next, the action plan unit 42 determinesif the acquired time corresponds to daytime (for example, between 7:00am and 6:00 pm) or to any other time. In the case of daytime, the timecoefficient is set to 1, and in other time, the time coefficient is setto a numerical value larger than 1 (for example, 1.2).

Then, the action plan unit 42 acquires the weather outside the vehicle.More specifically, the action plan unit 42 connects to an externalserver via the communication device 8, and acquires the weather at thecurrent location of the vehicle S. When the external camera 19 isprovided behind the windshield, the action plan unit 42 may analyze theimage captured by the external camera 19 by using a per se known imageanalysis means based on, for example, deep learning, and determines theweather. When the weather is rain, snow, hail, or fog, the action planunit 42 sets the weather coefficient to a numerical value larger than 1(for example, 1.2), and otherwise sets the weather coefficient to 1 (theweather coefficient is left unchanged). Thereafter, the action plan unit42 computes the product of the time coefficient and the weathercoefficient, and sets the product as the external object recognitioncoefficient. After that, the action plan unit 42 executes step ST14.

In step ST14, the action plan unit 42 computes a fellow occupantcoefficient. The fellow occupant coefficient is a numerical value of 1or more, and is set so as to increase monotonically with the number ofoccupants onboard other than the driver, or the number of fellowoccupants. In the present embodiment, the action plan unit 42 analyzesthe image captured by the internal camera 25 by using a per se knownimage analysis unit based on, for example, deep learning, and computesthe number of occupants. Next, the action plan unit 42 multiplies apredetermined positive numerical value (for example, 0.2) to the numberof fellow occupants, and adds 1 thereto as a fellow occupantcoefficient. When the computation of the fellow occupant coefficient iscompleted, the action plan unit 42 executes step ST15.

The action plan unit 42 computes a cumulative travel risk in step ST15.The cumulative travel risk is determined so as to increase monotonicallywith the travel distance (or travel time). Further, the cumulativetravel risk is determined so as to monotonically increase with theexternal object recognition coefficient and the fellow occupantcoefficient. In the present embodiment, as an example, the action planunit 42 computes the cumulative travel risk as the product of themileage, the external object recognition coefficient, and the fellowoccupant coefficient.

For example, in the daytime and under a fine weather (the externalobject recognition coefficient is 1), when only the driver is on board(the fellow occupant coefficient is 1), the cumulative travel risk iscomputed to be equal to the travel distance. After finishing thecomputation of the cumulative travel risk, the action plan unit 42 endsthe stop area determination process.

Next, a moving process is described in the following. In the movingprocess, the own vehicle travels from the start point of the stopprocess or one of the available stop areas to the next available stoparea. The action plan unit 42 may generate or invoke a following eventduring the moving process when a preceding vehicle traveling in the samedirection is detected. In the following event, the own vehicle followsthe preceding vehicle at a prescribed inter-vehicle distance. When nosuitable preceding vehicle is detected by the external camera 19, theaction plan unit 42 generates a constant speed traveling event so thatthe own vehicle travels at a prescribed constant speed. The action planunit 42 may be configured to generate a lane change event or the like asneeded.

Details of a stop position determination process which is executed inthe stop area are described in the following with reference to FIG. 4.

In the first step ST21 of the stop position determination process, theaction plan unit 42 extracts a position suitable for stopping in thestop area by using the image captured by the external camera 19, andsets the position as an available stop position.

Next, the action plan unit 42 executes step ST22. In step ST22, theaction plan unit 42 computes a stop risk. The stop risk is a numericalvalue of a possibility that a problem or a risky situation is likely tooccur when stopping the vehicle S at the available stop position.Examples of such a problem may include a case where the available stopposition has an obstacle, a case where some difficulty is encountered inentering the available stop position, and a case where there is a riskof collision with a nearby vehicle while moving to the available stopposition. The action plan unit 42 determines the stop risk such that thestop risk increases as the possibility of occurrence of a problem whenstopping the vehicle S at the available stop position and/or a severityof the problem that may be encountered increases. In the presentembodiment, the stop risk is set to 0 when the vehicle S can be broughtto a stop at the available stop position without any substantialproblem, and is set to 1 when the vehicle S cannot be brought to a stopat the available stop position.

In the present embodiment, the action plan unit 42 uses a per se knownimage analysis unit to analyze an image captured by the external camera19 to obtain a vehicle or the like located around the available stopposition, and computes a stop risk according to the captured image. Forexample, upon recognizing that there is already a parked vehicle at theavailable stop position, the action plan unit 42 determines that thevehicle S cannot be brought to a stop at this particular position, andsets the stop risk to 1. For example, when the available stop positionis set to a space having a sufficient area on the left side of astraight and flat road, and the vehicle S can be stopped without anyproblem and with a minimal risk, the action plan unit 42 sets the stoprisk to zero.

The action plan unit 42 may acquire the road information of the road onwhich the available stop position is selected from the map information,and compute the stop risk of the available stop position according tothe shape of the road. For example, when the available stop position islocated on a side of a curved road, the stop risk may be set closer to 1as the curvature increases. When the available stop position is locatednear a cliff, the stop risk may be set to approach 1. In this way, byreferring to the map information, it is possible to accurately andeasily evaluate the risk of stopping according to the shape and terrainof the road.

The action plan unit 42 acquires the inter-vehicle distance relative tothe following vehicle using at least one of the radar 17 and the lidar18. When the acquired inter-vehicle distance is equal to or less than anappropriate inter-vehicle distance (80 m in the present embodiment), theaction plan unit 42 computes the stop risk higher than when theinter-vehicle distance is larger than the appropriate inter-vehicledistance. This allows the risk of a rear end collision with thefollowing vehicle when stopping the vehicle to be reduced. The actionplan unit 42 may compute the stop risk to be lower when a followingvehicle is not detected than when a following vehicle is detected, andthe distance is equal to or less than the appropriate inter-vehicledistance.

Next, the action plan unit 42 executes step ST23. In step ST23, theaction plan unit 42 computes a stop threshold. The stop threshold is athreshold value which can be computed from the cumulative travel risk,and is compared with the stop risk of each available stop position todetermine if the vehicle should be brought to a stop at the particularstop position. In the present embodiment, the stop threshold isdetermined so as to increase monotonically with the cumulative travelrisk. For example, the action plan unit 42 may compute a value obtainedby multiplying 0.1 to the cumulative travel risk as the stop threshold.

Next, the action plan unit 42 executes step ST24. In step ST24, theaction plan unit 42 determines whether the stop risk is equal to or lessthan the stop threshold. The action plan unit 42 executes step ST25 whenthe stop risk is equal to or less than the stop threshold, and ends thestop position determination process without determining the stopposition when the stop risk is larger than the stop threshold. Thus, thecontrol unit 15 determines the available stop area at which thecumulative travel risk exceeds the stop risk as the final stop area.

Alternatively, the control unit may determine the available stop areaimmediately preceding the one at which the cumulative travel riskexceeds the stop risk as the final stop area.

The cumulative travel risk generally increases with the travelingdistance. The final stop area is selected as the last stop area wherethe cumulative travel risk does not exceed the stop risk. If youtraveled further to the stop area following the last stop area, thecumulative travel risk would have exceeded the stop risk.

In step ST25, the action plan unit 42 determines an available stopposition as the final stop position. Once the determination of the stopposition is completed, the action plan unit 42 ends the stop positiondetermination process.

Next, the mode of operation and effect of the vehicle control systemthus described above are discussed in the following with reference toFIG. 5. In the example of the movement of the vehicle S when the stopprocess is executed shown in FIG. 5, it is assumed that only the driveris onboard the vehicle, and it is in the daytime and in fine weather.

In the example shown in FIG. 5, the vehicle S is at the start position X(where the stop process is initiated), and there are four available stopareas A, B, C, and D along the route which are potentially suitable forbringing the vehicle to a stop. The table in FIG. 5 shows the distanceson the route from the start position X to the available stop areas A, B,C, and D. The distance from the start position X to the available stoparea A is the shortest so that the available stop area A is closest tothe vehicle at the start position X. The available stop areas B, C and Dare located at progressively greater distances from the start position Xalong the route in that order. The available stop area D is 10 km awayfrom the start position X along the route. An available stop positioncan be designated for each of the available stop areas A, B, C, and D.The available stop areas A, B, C, and D are connected by a road having asubstantially constant width, and there is no narrowing of the roadbetween the start position X and the last available stop area D. Theavailable stop area A and the available stop area C are both located inparts of the road where the curvature is large, and the stop risk ishigher in the available stop area A and the available stop area C thanin the available stop area B and the available stop area D. Further, itis assumed that the inter-vehicle distance with the following vehicle issufficiently large until the vehicle S comes to a stop.

When the stop process is initiated, the action plan unit 42 executes thestop area determination process at the start position X (ST3). In thestop area determination process, the action plan unit 42 selects theavailable stop area A closest to the vehicle S from the available stopareas A, B, C, and D as the currently selected stop area (ST11).Thereafter, the action plan unit 42 computes the distance (5 km) on theroute from the start position X to the stop area A (ST12). Thereafter,since the vehicle S is traveling in the daytime and under fine weather,the action plan unit 42 computes the external object recognitioncoefficient as 1 (ST13). Thereafter, since only the driver is on thevehicle S, the action plan unit 42 computes the fellow occupantcoefficient as 1 (ST14). Next, as shown in the table of FIG. 5, theaction plan unit 42 computes the cumulative travel risk for the stoparea A as 5 (ST15).

After that, the control unit 15 causes the vehicle S to automaticallytravel and move from the start position X to the stop area A. As thevehicle S moves into the stop area A (ST4), the action plan unit 42computes a stop risk at the available stop position in the stop area A(ST22). At this time, as shown in the table of FIG. 5, the stop risk isevaluated as 0.6. Thereafter, the action plan unit 42 computes the stopthreshold according to the cumulative travel risk (ST23), and comparesthe stop threshold with the stop risk (ST24). As shown in the table ofFIG. 5, the stop threshold is computed as 0.5, and the stop risk isevaluated as 0.6. Therefore, the action plan unit 42 determines that thestop risk is larger than the stop threshold, The stop positiondetermination process ends without determining the stop position.

Thereafter, as shown in FIG. 2, the action plan unit 42 determines thatthe stop position has not been determined (ST6), and performs the stoparea determination process once again (ST3). Thus, as shown in FIG. 5,the action plan unit 42 chooses the available stop area B closest to thevehicle S from the available stop areas B, C, and D as the stop area(ST11). Thereafter, the action plan unit 42 computes the distance (6 km)on the route from the start position X to the stop area B (ST12).Further, the action plan unit 42 computes the external objectrecognition coefficient and the fellow occupant coefficient both as 1(ST13, ST14). Next, as shown in the table of FIG. 5, the action planunit 42 computes the cumulative travel risk for the stop area B as 6(ST15), and ends the stop area determination process.

Next, the action plan unit 42 executes the moving process (ST4) to causethe vehicle S to travel from the available stop area A to the availablestop area B. At this time, when a preceding vehicle is detected by theexternal camera 19, the vehicle S follows the preceding vehicle, andtraces the trajectory which the preceding vehicle has followed.Accordingly, if there is an obstacle or the like on the road, thevehicle S can appropriately avoid the obstacle so that the vehicle S canbe more safely moved between the available stop areas.

When the vehicle S moves into the available stop area B, the action planunit 42 extracts an available stop position, and computes the stop risk(ST21, ST22). As shown in FIG. 5, the available stop area B is locatedalong a straighter road than the available stop area A. Thus, the stoprisk in the available stop area B is lower than that in the availablestop area A, and the stop risk is evaluated to be 0.2 as shown in thetable of FIG. 5. Thereafter, the action plan unit 42 computes the stopthreshold (ST23). At this time, since the cumulative travel risk iscomputed as 6, the stop threshold is evaluated as 0.6. Next, the actionplan unit 42 compares the stop threshold with the stop risk (ST24).Since the stop threshold is 0.6 and the stop risk is 0.2, the actionplan unit 42 determines the available stop position as the stopposition, and ends the stop position determination process. Thereafter,the stop execution process (ST7) is executed, and the vehicle S isbrought to a stop at the stop position in the available stop area B asshown in FIG. 5.

As discussed above, when the vehicle S cannot be brought to a stop inthe available stop area (available stop area A), the vehicle Sautonomously travels to another available stop area (available stop areaB), and comes to a stop in the available stop area which has become thefinally selected stop area. Thus, if there is no suitable stop positionin the provisionally selected stop area, the vehicle S travels on to thenext available stop area. If the next available stop area is found toprovide a suitable stop position, this available stop area is selectedas the final stop area, and the vehicle S is brought to a stop at thesuitable stop position in the finally selected stop area. Thus, thevehicle S can be brought to a stop is a suitable location in a highlyreliable manner.

The action plan unit 42 selects the stop area and the stop position bycomparing the stop threshold with the stop risk. Therefore, the vehicleS can be brought to a stop at a position where the smallest possiblerisk is involved.

The stop threshold increases monotonically with the cumulative travelrisk, and the cumulative travel risk increases monotonically with themileage. Therefore, the stop threshold monotonously increases with thetravel distance. On the other hand, the stop risk is set to a value of 0to 1 depending on the situation of each available stop area. Since thevehicle S comes to a stop as soon as the stop risk becomes equal to orless than the stop threshold, the travel distance which vehicle travelsuntil the vehicle comes to a stop is at most limited to the distancefrom the start position X to the stop area where the stop threshold is 1or more (the D region in FIG. 5B) without regard to the conditions inthe intervening available stop areas. Therefore, the vehicle S can bereliably brought to a stop without the fear of allowing the vehicle S tocontinue to travel over an unduly long distance.

FIG. 6 schematically shows the movement of the vehicle S when the stopprocess is started at the same start position X similarly as in FIG. 5.Only the driver in onboard the vehicle S, and it is at night and rainy.FIG. 6 also includes a table showing the distance on the route, thecumulative travel risk, the stop threshold, and the stop risk for eacharea similarly as in the table of FIG. 5.

The action plan unit 42 executes the stop area determination process atthe start position X, and provisionally selects the available stop areaA as the stop area. Further, the action plan unit 42 computes thedistance on the route from the start position X to the available stoparea A and the associated cumulative travel risk. However, since it isnighttime and rainy, the external object recognition coefficient is1.2×1.2=1.41 so that the cumulative travel risk is 1.41 times greaterthan in the case of daytime and fine weather (as was the case in theexample of FIG. 5).

When the vehicle S reaches the available stop area A, the action planunit 42 computes the stop threshold and the stop risk, and comparesthem. At this time, as shown in the table of FIG. 6, the stop thresholdin the available stop area A is 0.705 and the stop risk is 0.6 so theaction plan unit 42 determines the available stop position in theavailable stop area A as the finally selected stop position. As aresult, the vehicle S comes to a stop at this stop position which iscloser to the start position X than the stop position selected in thedaytime and under fine weather.

When the brightness of the image taken by the external camera 19 is lowand the road sign is difficult to detect, such as at night, when theweather is poor due to rain, snow, hail, or fog, the external objectrecognition coefficient is set to be larger than 1. As a result, therate of increase in the cumulative travel risk per unit travel distanceat night is greater than in daytime. In addition, the rate of increasein the cumulative travel risk per unit travel distance in rainy weatheris greater than in sunny weather. As a result, the stop threshold atnight or in the rain, snow, hail, or fog increases, and the vehicle Stends to be brought to a stop at a position closer to the start positionX. Therefore, when it is difficult to detect the road signs, the traveldistance to the stop area tends to be reduced, and the safety of thevehicle S can be enhanced. Further, since the external objectrecognition coefficient can be computed according to the time of the dayand the weather, the external object recognition coefficient can becomputed without any difficulty.

When there is a fellow occupant, the fellow occupant coefficient is setto a value larger than 1, and the increase rate of the cumulative travelrisk per unit travel distance increases. As a result, the cumulativetravel risk and the stop threshold increase more rapidly so that thevehicle S tends to be brought to a stop at a position closer to thestart position X. Therefore, the vehicle S can be brought to a stop morequickly when there is a fellow occupant. As a result, the fellowoccupant is able to take over the driving with a minimum delay.

When the distance to the following vehicle is equal to or less than theappropriate inter-vehicle distance, the action plan unit 42 computes thestop risk to be smaller when the inter-vehicle distance is larger thanthe appropriate inter-vehicle distance than when the inter-vehicledistance is equal to or smaller than the appropriate inter-vehicledistance. Therefore, when the inter-vehicle distance to the followingvehicle is short and the danger of a collision by the following vehicleas the vehicle comes to a stop is significant, the stop risk isincreased. Thus, when the risk of collision by the following vehicle ishigh and the stop risk is greater than the cumulative travel risk, thecollision of the following vehicle can be avoided by causing the vehicleS to continue traveling.

Second Embodiment

The vehicle control system 101 according to the second embodimentdiffers from the vehicle control system 1 of the first embodiment onlyin the steps ST12 and ST15 of the stop area determination process, andthe other parts are the same. The description of the other parts isomitted.

In step ST12, the action plan unit 42 computes an effective distance onthe route from the start position X to each available stop area, insteadof the actual distance on the route from the start position to the stoparea. The effective distance is a distance that takes into account thedifficulty in traveling. For example, upon determining that there is anarrowing of the road on the route, the action plan unit 42 increasesthe effective distance according to the distance of the narrowed part ofthe road and/or the extent of the narrowing of the road.

For instance, the action plan unit 42 may determine the effectivedistance as (the distance on the route from the start position to theavailable stop area)+(the distance of the narrowed part of theroad)×(the factor of narrowing). The narrow road factor may be varieddepending on the width of the narrowed part of the road, and may be setto a value of 0.01 or more and 0.10 or less. Alternatively, the actionplan unit 42 may determine the effective distance by detecting thedistance of a narrow part of the road which is no more than a certainthreshold such as 4 m, and multiplying a certain factor to the length ofthe narrow part of the road when computing the effective distance.

In step ST15, the action plan unit 42 computes the cumulative travelrisk as the product of the effective distance, the external objectrecognition coefficient, and the fellow occupant coefficient.

Next, the advantage of the vehicle control system 101 configured asdescribed above are discussed in the following follows. The cumulativetravel risk for each available stop area is greater when there is anarrowing of the road than when there is no narrowing of the road.Thereby, the travel distance of the vehicle S tends to be reduced wherethere is a narrowing of the road so that the vehicle S can be stoppedmore quickly.

Third Embodiment

The vehicle control system 201 according to the third embodiment differsfrom the vehicle control system 1 of the first embodiment only in thesteps ST12 and ST15 of the stop area determination process, and theother parts are the same. The description of the other parts is omitted.

In step ST12, the action plan unit 42 computes the travel time requiredfor the vehicle to travel from the start position to each available stoparea, instead of the distance on the route from the start position tothe stop area.

In step ST15, the action plan unit 42 computes the cumulative travelrisk as the product of the travel time, the external object recognitioncoefficient, and the fellow occupant coefficient.

Next, the advantages of the vehicle control system 201 configured asdescribed above are discussed in the following. Since the cumulativetravel risk can be computed according to the time spent in the travellane, the cumulative travel risk can be computed according to the riskassociated with the traveling of the vehicle S. Further, as the traveltime becomes longer, the cumulative travel risk increases. Therefore,the travel time of the vehicle S can be shortened so that the vehicle Scan be stopped more quickly.

Fourth Embodiment

The vehicle control system 301 according to the fourth embodimentdiffers from the vehicle control system 1 of the first embodiment in themethod of calculating the stop risk in step ST22 of the stop positiondetermination process. The other parts of the vehicle control system 301according to the fourth embodiment are the same as those of the vehiclecontrol system 1 of the first embodiment, and a description thereof willnot be repeated.

In the vehicle control system 1 according to the first embodiment, theaction plan unit 42 added a predetermined value when the distance to thefollowing vehicle is equal to or less than the appropriate inter-vehicledistance, compared to when the distance is larger than the appropriateinter-vehicle distance. On the other hand, in the vehicle control system301 according to the fourth embodiment, the stop risk is computed to begreater when the following vehicle is detected by the vehicle sensor 7than when the following vehicle is not detected by the vehicle sensor 7.The vehicle sensor 7 in this embodiment may include the external camera19 for monitoring the rear of the vehicle, and the detection range ofthe external camera 19 for detecting following vehicles may be about 100m. When the computation of the stop risk is completed, the action planunit 42 executes step ST23.

The advantages of the vehicle control system 301 configured as describedabove are discussed in the following. If a following vehicle is detectedbehind the vehicle, the risk of stopping is computed to be higher.Accordingly, when a following vehicle is detected behind the vehicle, orin other words, when there is a possibility of a rear end collision bythe following vehicle, the vehicle is made less likely to be brought toa stop, and the safety of the vehicle is improved. In addition, sincethe stop risk is computed according to the presence or absence of thefollowing vehicle, the configuration is simpler than in the case wherethe stop risk is computed according to the inter-vehicle distance.

Fifth Embodiment

The vehicle control system 401 according to the fifth embodiment differsfrom the vehicle control system 1 of the first embodiment in the methodof calculating the stop risk in step ST22 of the stop positiondetermination process. The other parts of the vehicle control system 401according to the fifth embodiment are the same as those of the vehiclecontrol system 1 of the first embodiment, and thus description thereofwill be omitted.

In the vehicle control system 401 according to the fifth embodiment,when the vehicle is about to reach an available stop area, the actionplan unit 42 determines if the vehicle is traveling in a passing lane(or a fast lane) according to the current position of the vehicle andthe map information acquired by the navigation device 9. When thevehicle is traveling in the passing lane, a predetermined value is addedto the stop risk, thereby computing a greater stop risk than when nottraveling in the passing lane. When the computation of the stop risk iscompleted, the action plan unit 42 executes step ST23.

The effect of the vehicle control system 401 configured as describedabove will be described. If the vehicle is traveling in the passing lanewhen the vehicle is about to reach the stop area, it is necessary tochange lanes or the like before bringing the vehicle to a stop. In thevehicle control system 401, the risk of stopping is computed to behigher when the vehicle is traveling in the passing lane than when thevehicle is traveling in a travel lane (a slow lane), and the vehicle maycontinue to travel to a newly available stop area without stopping.Thus, the vehicle can be stopped more safely.

Sixth Embodiment

The vehicle control system 501 according to the sixth embodiment differsfrom the vehicle control system 1 of the first embodiment in the methodof calculating the stop risk in step ST22 executed by the action planunit 42. The rest of the configuration of the vehicle control system 501according to the sixth embodiment is the same as the vehicle controlsystem 1 of the first embodiment, and the description thereof will notbe repeated.

In the vehicle control system 501 according to the sixth embodiment, theaction plan unit 42 determines if each of the available stop areas iswithin an area where there is a restriction in the travel lane in stepST12. The area where the travel lane is restricted may be, for example,within a predetermined range from an entrance or an exit of a road ramp,or may be within a predetermined range from a point where a roadconstruction is underway. The action plan unit 42 computes thecorresponding stop risk to be larger when the stop area is locatedwithin the area where the travel lane is restricted than when the stoparea is located outside of the area where the travel lane is restricted.When the computation of the stop risk is completed, the action plan unit42 executes step ST23.

The advantages of the vehicle control system 501 configured as describedabove are discussed in the following. When there is an available stoparea within the area where the travel lane is restricted, the stop riskis increased as compared with the case where the vehicle is outside thearea where the travel lane is restricted. This allows the vehicle tocome to a stop outside of the area where the vehicle may be congestedowing to the restriction in the travel lane. Therefore, the traffic ofthe surrounding vehicles are prevented from being obstructed, and thevehicle can be brought to a stop more safely.

Seventh Embodiment

The vehicle control system 601 according to the seventh embodimentdiffers from the vehicle control system 1 of the first embodiment in themethod of calculating the cumulative travel risk in step ST15 executedby the action plan unit 42. The other parts of the vehicle controlsystem 601 according to the sixth embodiment are the same as those ofthe vehicle control system 1 of the first embodiment, and thusdescription thereof will be omitted.

In the vehicle control system 601 according to the seventh embodiment,the map information stored by the navigation device 9 includes theresults of lane changes of the surrounding vehicles. The history of thelane changes of the surrounding vehicles means the number of times thelane changes are performed by the surrounding vehicles during aprescribed period of time in the past in each of prescribed places onthe roads along the route. The number of times the lane changes havebeen performed may be computed in advance by, for example, a roadmanager according to data on the movement of the vehicles over theprescribed time period acquired by an observation camera provided on theroad. Generally, the number of times the lane changes of the surroundingvehicles are performed within a predetermined period of time in mergingroads, branch roads and the likes tend to be greater than in other partsof the roads.

In step ST15, the action plan unit 42 obtains the history of the lanechanges of the surrounding vehicles at each point on the route from thestart position of the stop process to each of the available stop areas.Thereafter, along the route from the start position of the stop processto the arrival at each available stop area, the action plan unit 42computes the total sum of the number of lane changes of the surroundingvehicles performed within a predetermined period at each point on theroute. The action plan unit 42 then computes the cumulative travel riskaccording to the computed total number of times of lane changes of thesurrounding vehicles. In the present embodiment, as the sum of thenumber of lane changes of the surrounding vehicles increases, thecumulative travel risk is computed to be larger. When the computation ofthe cumulative travel risk is completed, the action plan unit 42 endsthe stop area determination process.

The advantages of the vehicle control system 601 configured as describedabove are discussed in the following. If the total number of lanechanges of the surrounding vehicles on the route from the start positionof the stop process to the arrival at each available stop areaincreases, the cumulative travel risk increases. Therefore, the riskarising from the lane changes of the surrounding vehicles is taken intoaccount in computing the cumulative travel risk, and the cumulativetravel risk involved for the vehicle to travel from the start positionto each available stop area can be appropriately computed. As describedabove, when the total number of lane changes increases, the cumulativetravel risk is computed to be larger so that a route in which the lanechanges of the surrounding vehicle are frequent can be avoided so thatthe vehicle can be brought to a stop more safely.

The present invention has been described in terms of specificembodiments, but is not limited by such embodiments, and can be modifiedin various ways without departing from the spirit of the presentinvention. The cumulative travel risk was represented by the product ofvarious coefficients and the travel distance, but the present inventionnot limited to this mode. The cumulative travel risk may also becomputed in a different manner so that the cumulative travel riskmonotonically increases with respect to the travel distance, the traveltime, the effective distance, and various coefficients.

In the above embodiments, the external object recognition coefficientwas determined according to time and weather, but the present inventionis not limited to this mode. For example, the external objectrecognition coefficient may be computed by comparing the shape of theroad sign included in the road information with the shape of the roadsign acquired by the external camera 19, and quantifying the degree ofcoincidence between the two. At this time, the external objectrecognition coefficient may be set to be close to 1 when the degree ofcoincidence is high, and to be larger than 1 when the degree ofcoincidence is low.

In the above embodiments, the cumulative travel risk was computed in thestop area determination process, but the present invention is notlimited to this mode. For example, the cumulative travel risk may becomputed in the stop position determination process. At this time, thecumulative travel risk may be computed as a risk taken by the vehicle Sbefore reaching the stop position, or in other words, the cost that isincurred until the vehicle S reaches the stop position. At this time,the vehicle control system may either compute the final cumulativetravel risk at the start of the stop process or compute the currentcumulative travel risk or revise the earlier computations as the vehicleprogresses toward the final stop area. In the latter case, changes inthe conditions of the road, the weather and the time of the day can beaccounted for in the computation of the cumulative travel risk.

In the above embodiments, the action plan unit 42 computed thecumulative travel risk as the product of the mileage, the externalobject recognition coefficient, and the fellow occupant coefficient, butthe present invention is not limited to this mode. The action plan unit42 may be configured to compute the cumulative travel risk strictlyaccording to the travel distance, and the vehicle control system 1 maynot include the occupant monitoring device 11.

In the above embodiments, the action plan unit 42 computed the stop riskaccording to the distance between the vehicle and the following vehicle,but the present invention is not limited to this mode. The action planunit 42 may compute the stop risk according to the distance between thevehicle and any nearby vehicle or the distance between the own vehicleand a vehicle traveling along a side of the own vehicle. In particular,if the action plan unit 42 computes the stop risk according to thedistance to the vehicle traveling on the left side, the risk associatedwith the presence of the vehicle on the left side of the own vehicle canbe properly taken into account because the own vehicle will be requiredto change lanes to the left lane before coming to a stop at theavailable stop area.

The invention claimed is:
 1. A vehicle control system, comprising: acontrol unit for steering, accelerating, and decelerating a vehicle; anoccupant monitoring device configured to monitor a driver of thevehicle; an external environment recognition device configured toacquire information on an environment surrounding the vehicle; and a mapdevice retaining map information; wherein the control unit is configuredto execute a stop process by which the vehicle is parked in a prescribedstop area when it is detected that the control unit or the driver hasbecome incapable of properly maintaining a traveling state of thevehicle, and wherein, in the stop process, the control unit determines aplurality of available stop areas according to the information on theenvironment surrounding the vehicle and the map information, andcomputes, for each available stop area, a cumulative travel riskobtained by accumulating a travel risk involved in traveling from aposition of the vehicle when the stop process is initiated to eachavailable stop area and a stop risk in stopping in each available stoparea, the control unit determining an available stop area immediatelypreceding the one at which the cumulative travel risk exceeds the stoprisk as a final stop area by comparing the cumulative travel risk withthe stop risk in each available stop area sequentially from the nearestone.
 2. The vehicle control system according to claim 1, wherein when apreceding vehicle is detected by the external environment recognitiondevice, the control unit causes the vehicle to follow the precedingvehicle in each interval between adjoining available stop areas.
 3. Thevehicle control system according to claim 1, wherein the control unitobtains the cumulative travel risk as increasing monotonically with atravel distance or a travel time.
 4. The vehicle control systemaccording to claim 1, wherein the external environment recognitiondevice is configured to capture an image of road signs, and the controlunit increases the cumulative travel risk as the image of road signsgrows darker.
 5. The vehicle control system according to claim 1,wherein the control unit increases the cumulative travel risk for eachunit travel distance more at night than in daytime.
 6. The vehiclecontrol system according to claim 1, wherein the control unit increasesthe cumulative travel risk for each unit travel distance more on a rainyday than on a fine day.
 7. The vehicle control system according to claim1, wherein the occupant monitoring device is configured to detect anoccupant other than a driver, and the control unit increases thecumulative travel risk for each unit travel distance more when theoccupant other than the driver is detected than when the occupant otherthan the driver is not detected.
 8. The vehicle control system accordingto claim 1, wherein the external environment recognition device isconfigured to detect a following vehicle, and the control unit increasesthe cumulative travel risk for each unit travel distance more when thefollowing vehicle is detected as the vehicle is about to come to a stopin the next available stop area than when the following vehicle is notdetected.
 9. The vehicle control system according to claim 8, whereinthe external environment recognition device is configured to detect aninter-vehicle distance between the vehicle and a following vehicle, andthe control unit increases the cumulative travel risk for each unittravel distance more when the inter-vehicle distance between thefollowing vehicle and the vehicle is equal to or lower than a prescribedvalue than when the inter-vehicle distance is greater than theprescribed value.
 10. The vehicle control system according to claim 1,wherein the control unit increases the cumulative travel risk for eachunit travel distance more when the vehicle is traveling in a fast lanethan when the vehicle is traveling in a slow lane.
 11. The vehiclecontrol system according to claim 1, wherein the control unit increasesthe cumulative travel risk in a part of a road where lanes arerestricted.
 12. The vehicle control system according to claim 1, whereinthe control unit determines the stop risk at each available stop areafrom the map information.
 13. The vehicle control system according toclaim 1, wherein the control unit increases the cumulative travel riskin a narrow part of a road.
 14. The vehicle control system according toclaim 1, wherein the control unit increases the cumulative travel riskin a part of a route where past data indicates a high frequency of lanechanges.
 15. A vehicle control system, comprising: a control unit forsteering, accelerating, and decelerating a vehicle; an occupantmonitoring device configured to monitor a driver of the vehicle; anexternal environment recognition device configured to acquireinformation on an environment surrounding the vehicle; and a map deviceretaining map information; wherein the control unit is configured toexecute a stop process by which the vehicle is parked in a prescribedstop area when it is detected that the control unit or the driver hasbecome incapable of properly maintaining a traveling state of thevehicle, and wherein, in the stop process, the control unit determines aplurality of available stop areas according to the information on theenvironment surrounding the vehicle and the map information, andcomputes, for each available stop area, a cumulative travel riskobtained by accumulating a travel risk involved in traveling from aposition of the vehicle when the stop process is initiated to eachavailable stop area and a stop risk in stopping in each available stoparea, the control unit determining a final stop area by comparing thecumulative travel risk with the stop risk in each available stop areasequentially from the nearest one, and wherein the occupant monitoringdevice is configured to detect an occupant other than a driver, and thecontrol unit increases the cumulative travel risk for each unit traveldistance more when the occupant other than the driver is detected thanwhen the occupant other than the driver is not detected.
 16. The vehiclecontrol system according to claim 15, wherein the control unitdetermines the available stop area at which the cumulative travel riskexceeds the stop risk as the final stop area.
 17. A vehicle controlsystem, comprising: a control unit for steering, accelerating, anddecelerating a vehicle; an occupant monitoring device configured tomonitor a driver of the vehicle; an external environment recognitiondevice configured to acquire information on an environment surroundingthe vehicle; and a map device retaining map information; wherein thecontrol unit is configured to execute a stop process by which thevehicle is parked in a prescribed stop area when it is detected that thecontrol unit or the driver has become incapable of properly maintaininga traveling state of the vehicle, and wherein, in the stop process, thecontrol unit determines a plurality of available stop areas according tothe information on the environment surrounding the vehicle and the mapinformation, and computes, for each available stop area, a cumulativetravel risk obtained by accumulating a travel risk involved in travelingfrom a position of the vehicle when the stop process is initiated toeach available stop area and a stop risk in stopping in each availablestop area, the control unit determining a final stop area by comparingthe cumulative travel risk with the stop risk in each available stoparea sequentially from the nearest one, and wherein the externalenvironment detection device is configured to detect a followingvehicle, and the control unit increases the cumulative travel risk foreach unit travel distance more when the following vehicle is detected asthe own vehicle is about to come to a stop in the next available stoparea than when the following vehicle is not detected.
 18. The vehiclecontrol system according to claim 17, wherein the control unitdetermines the available stop area at which the cumulative travel riskexceeds the stop risk as the final stop area.